It is known, in particular from French patent application 91 03412, to provide a heat exchanger tube comprising: a tube body having an oblong cross section defined by two major faces and two minor faces; an end portion of oblong cross section defined by two major faces and two minor faces; and a transition portion joining the tube body and end portion together, with the cross section of the tube body having a length and a width which are respectively greater and less than the length and width, respectively, of the cross section of the end portion.
In tubes of that type, the major faces of the body and end portion may be flat or slightly curved, while the minor faces of the tube body and those of the end portion are generally semicircular or even flat, in which case this flat minor face is joined to the two major faces through two rounded portions having a small radius of curvature. These tubes are arranged in a conventional way so as to form a tube bundle which is provided with fins, and over which a stream of air is passed. The oblong form of the tube bodies facilitates the flow of this air and reduces energy losses, by comparison with conventional heat exchangers having round tubes.
The cross section of the end portion of each tube is less oblong than that of the associated tube body, so as to facilitate the fitting of the tube end portion on to a header plate, or "perforated plate", through which the tube end portions are inserted.
In the heat exchanger described in the above mentioned French patent application, the tubes may be disposed in pairs and in two rows, with the end portions of the tubes of a pair being received in a common hole in the header plate. This particular arrangement enables a more compact configuration of the heat exchanger to be achieved, especially widthwise, because the tubes are abutted together in pairs instead of being separated from each other as in previous arrangements.
One of the problems posed by the arrangement of tubes of the kind just described is that of how to configure, or work, them to the required form, especially as regards the transition portion of the tube. It is important that the tubes should be made using a forming apparatus which is as simple as possible, and which enables them to be made on a large scale quantity production basis.
At the same time it is essential that the transition portion of the tube should be made as short as possible in the axial direction, due to the fact that the cooling fins of the heat exchanger lie only along the bodies of the tubes.